The Probe Feed Patch Antenna

Transcription

1 Finite Element Tutorial in Electromagnetics #1 DRAFT Sponsored by NSF Grant #05-559: Finite Element Method Exercises for use in Undergraduate Engineering Programs The Probe Feed Patch Antenna Prepared By: Dr. Vladimir A Labay, Department of Electrical and Computer Engineering Gonzaga University, Spokane, Washington Estimated time to complete This tutorial: 60 minutes

2 Outline of Tutorial 1. Introduction 2. Overview of computational electromagnetics (CEM) Maxwell s Equations and their numerical approximation Full-wave CEM techniques The method of moments (MoM) The finite difference time domain (FDTD) Method The finite element method (FEM) 3. The CEM modeling process Overview Methods of CEM Problems and Limitations 4. Finite Element Method (FEM) Introduction and Overview Strengths and Weaknesses Weaknesses 2

3 Outline of Tutorial (con t) 5. Ansoft s High Frequency Structure Simulator (HFSS) Introduction Using HFSS to create and improve designs 6. Problem Definition: The Probe Feed Patch Antenna Basic Characteristics of Microstrip/Patch Antennas Design Equations based on the Transmission Line Model Sample Design 7. Step-by-Step Solution Launching Ansoft HFSS Set up the Design Creating a Model Set up and Generate Solutions Analyze and display results 8. Further Reading and References 3

4 Tutorial Objectives Understand the basis of FE theory for three-dimensional electromagnetic analysis. (PEO #1) Understand the fundamental basis of the radiation field pattern in a patch antenna beam through the use of Ansoft s High Frequency Structure Simulator (HFSS) three-dimensional finite element software. (PEO #2) Be able to construct a correct solid model using the build in 3-D solid modeler and perform a correct three-dimensional finite element analysis using HFSS solution engine. (PEO #3) Be able to interpret and evaluate finite element solution quality including verifying convergence criterion and field plots. (PEO #4) 4

5 Overview of Computational Electromagnetics (CEM) Electromagnetics The study of electrical and magnetic fields and their interaction Governed by Maxwell s Equations (Faraday s Law, Ampère s Circuital Law, and Gauss Laws) Maxwell s Equations relate the following Vector and Scalar Fields E: the Electric Field Intensity Vector (V/M) H: the Magnetic Field Intensity Vector (A/m) D: the Displacement Flux Density Vector (C/m 2 ) B: the Magnetic Flux Density Vector (T) J: the Current Density Vector (A/m 2 ) ρ: the Volume Charge Density (C/m 3 ) μ: is the Permeability of the medium (H/m) ε: the Permittivity of the medium (F/m) 5

6 Maxwell s Equations B Faraday s Law: E = 0 = t B Gauss Laws: D = ρ Ampère s Circuital Law: H = J+ D t Constitutive Equations: B = μ H D = ε E Actual solution complex and for realistic problems require approximations Numerical approximations of Maxwell s equations is known as computational electromagnetics (CEM) 6

7 Applications of CEM Over the past five decades CEM has been successfully applied to several engineering areas, including: Antennas Biological electromagnetic (EM) effects Medical diagnosis and treatment Electronic packaging and high speed circuits Superconductivity Microwave devices and circuits Law enforcement Environmental issues Avionics Communications Energy generation and conservation Surveillance and intelligence gathering Homeland Security Signal Integrity 7

8 Full-wave CEM techniques Approximations of Maxwell s equations may be classified into several categories, e.g., low-frequency, quasi-static, full-wave, lumped element equivalent, etc. This tutorial deals with the finite element method a full-wave technique. Full-wave techniques have the potential to be the most accurate of all numerical approximations because they incorporate all higher order interactions and do not make any initial physical approximations Examples include: Finite difference time domain (FDTD) Method Method of Moments (MoM) Method Finite Element (FEM) Method Transmission Line Matrix (TLM) Method The Method of Lines (MoL) The Generalized Multipole Technique (GMT) The FDTD, MoM and FEM are the most popular today! 8

9 Full-wave CEM techniques (con t) Central to all methods is the idea of discretizing some unknown electromagnetic property, for example: MoM: the Surface Current FE: the Electric Field FDTD: the Electric and Magnetic Field Discretization is also known as meshing that subdivides the geometry in a large number of elements Two dimensional elements: triangles Three dimensional elements: tetrahedral Within each element, a simple functional dependence (basis functions) is assumed for the spatial variation of the unknown The amplitude and phase of the unknown quantity is determined by the application of the particular CEM 9

10 Limitations of Full-wave CEM techniques CEM is a modeling process and therefore a study in acceptable approximation In other words, CEM replaces a real field problem with an approximate one which causes limitations and problems that one must keep in mind Limitations of the mathematical model and Simplifications in the formulation Assumptions are generally made, e.g., assuming an infinite ground plane in an antenna structure. Are the assumption valid? Have you made simplifications on the design that are not valid? For example, simplifying a thin wire by a current filament. Tolerances and Manufacturing deviations Tolerances are a part of all manufactured devices. How do small changes in dimensions or material properties affect the performance? Do other manufacturing considerations, other that tolerances, affect the performance? Finite Discretization Is the mesh fine enough to properly so that the basis functions can adequately represent the fields? Numerical approximations and Finite machine precision Does double precision provide enough accuracy for your problem, especially if it is ill conditioned? 10

11 Finite Element Method Overview Initially used in structural mechanics and thermodynamics dating back to the 1950 s First application in electromagnetics appeared in literature in the late 1960 s but did not see widespread adoption until the 1980 s A problem of spurious modes was not solved until the 1980 s through a theoretical breakthrough with edge elements Widespread availability of powerful main-frame and personal computers also aided the expansion Starts with the partial differential equation (PDE) form of Maxwell s Equations Solution can be viewed from two main perspectives Variational analysis Finds a variational functional whose minimum corresponds to the solution of the PDE Weighted residuals Introduces a weighted residual or error and using Green s function, shift one of the differentials in the PDE to the weighting functions In most applications these two viewpoints result in identical equations 11

12 Finite Element Method (con t) FEM can handle essentially two different types of EM problems Eigenanalysis (source-free) Deterministic (driven) FEM does not include a radiation condition Open regions, such as antennas (see below), requires special treatment Introduction of a artificial absorbing region within the mesh Example Microstrip Patch Antenna Antenna Patch Artificial absorbing region (box surrounding the antenna) Infinite Ground Plane Substrate Material 12

13 Finite Element Method (con t) Strengths Handles complex geometries and material inhomogeneities easily Handles dispersive or frequency-dependent materials easily Handles eigenproblems easily Has better frequency scaling characteristics that MoM (but usually requires a larger set of unknowns) Easily applicable to multi-physics problems by coupling solutions in thermal or mechanical to the EM solution Weaknesses Inefficient treatment of highly conducting radiators when compared to the MoM FEM meshes become very complex for large 3-D structures More difficult to implement than the FDTD thus limiting their use in commercial software. Little code development is done by engineers Efficient preconditioned iterative solvers are required when higher-order elements are used. Again, restricting the code development by individual engineers 13

14 Commercial FEM EM Software Some Companies that market commercial FEM EM software: Ansoft Corporation, Inc. High frequency structure simulator (HFSS) Ansys, Inc. Emag Comsol, Inc. COMSOL Multiphysics with Electromagnetics Module SolidWorks Corporation COSMOSEMS HFSS by Ansoft will be used solely in this tutorial 14

15 Ansoft HFSS Overview HFSS is a high-performance full-wave electromagnetic field simulator for arbitrary 3D volumetric passive device modeling that takes advantage of the familiar Microsoft Windows graphical user interface. It integrates simulation, visualization, solid modeling, and automation in an easy-to-learn environment. HFSS includes: A graphical interface to simplify design entry A field solving engine with accuracy-driven adaptive solutions Powerful post processor for displaying currents, fields and RF parameters Automatic and adaptive mesh generation and refinement and tangential vector finite elements Macro feature allows for users to log sessions of design or simulation to an easy to read file (useful in creating a library of structure based on a nominal structure) A comprehensive materials database that contains permittivity-, permeability, electric-, magnetic-loss tangents for common materials. Typical HFSS Uses PCB Board Modeling: Power and Ground Planes, Backplanes EMC/EMI: Shield Enclosures, Coupling, Near- and Far- Radiation Antennas/Mobile Communications: Patches, Horns, Radar Cross Section Connectors: Coaxial (Coax), Transitions Waveguide: Filters, Resonators, Transitions, Couplers 15

16 Problem Definition The Probe Feed Patch Antenna The following tutorial is intended to show how to create, simulate, and analyze a probe feed patch antenna using the Ansoft HFSS Design Environment This tutorial leads you step-by-step through the design of a Probe Feed Patch Antenna. By following the steps in this tutorial you will be able to: Draw a geometric model Modify a model s design parameters Assign variables to a model s design parameters Specify solution settings for a design Validate a design s setup Run a HFSS simulation Create a 2-D plot of the antenna radiation pattern Create a 3-D plot of the antenna radiation pattern Create a field overlay plot of the results Study the mesh created by HFSS for the solution Create a phase animation of the results 16

17 Problem Background Uses of Patch Antennas Low-profile antennas are used in high-performance aircraft, spacecraft, satellite, mission applications, and mobile radio and wireless communications, where size, weight, cost, performance, ease of installation, and aerodynamic profile are constraints. Advantages of Patch Antennas for these uses Patch (or sometimes called Microstrip) Antennas are low profile, conformable to planar and non-planar surfaces, simple and inexpensive to manufacture using modern printed circuit technology, mechanically robust when mounted on rigid surfaces and very versatile in terms of resonant frequency, polarization, pattern, and impedance. 17

18 Problem Background (con t) Basic Characteristics A metallic strip or patch mounted on a dielectric layer (substrate) which is supported by a ground plane Typically, the both the thickness of the metallic strip and the spacing between the patch and the ground plane are small, as compared to the free space wavelength (t << λ and h << λ ). Recall λ=v/f where v is the velocity of propagation in free space (3x10 8 m/s) and f is the frequency of operation Typically designed for broadside radiation (radiation pattern is normal to the patch For rectangular patches, the length is usually between one-third and one-half of the free space wavelength Popular feed techniques for Patch Antennas Microstrip line (shown on previous slide), Probe (this tutorial), Aperture coupling and Proximity coupling Possible Analysis models Transmission-line model Easiest, gives good physical insight Full-wave Analysis FEM (this tutorial), FDTD, MoM Very complex, very accurate, very versatile 18

19 Patch Antenna Design For this tutorial we will design the patch antenna using the approximate equations developed by the transmission line model and then verify the design using the FEM method. You will notice a slight change in performance characteristics of the antenna from the full-wave analysis to the transmission line calculations. The FEM analysis is much more accurate. The following is a step-by-step guide to calculate the dimensions of the patch. Step 1: Specify the relative dielectric constant of the substrate, ε r, the resonant frequency of the patch, f r, and the height of the substrate, h. Step 2: Calculate the width, W, of the patch using the following equation: W = c 2 2 ε + 1 f r r 19

20 Patch Antenna Design (con t) Step 3: Determine the effective constant of the Microstrip antenna using: ε eff εr + 1 εr 1 = h W 1 2 Step 4: Determine the extension of the length, ΔL, using: ΔL h = ( ε ) eff W h W ( ε ) Step 5: Determine the actual length of the patch. c L = 2ΔL 2 f ε eff r eff h 20

21 Design Example Design a rectangular Microstrip antenna using Rogers RT/duroid 5880 with a dielectric constant of 2.2 with a height of 3.2 mm so as to resonate at 2.97 GHz. Solution: W = 100 = 4. 0 cm ε eff = + + = ( ) ΔL = ( 0. 32)( ) = cm 4. 0 ( ) L = 100 2( ) = 3. 2 cm

22 Conventions used in this Tutorial Main Procedures are presented in Bold. Detailed procedures and indicated by a numbered list after the main procedure. Notes are in italics. Bold type is used for the following: Keyboard entries that should be typed in their entirety exactly as shown. For example, Inf_GND means to type the Inf followed by a underscore then type GND Om screen prompts and messages, names of options and text boxes, and menu commands. For example, click Edit>Select>By name Labeled keys on the computer keyboard. For example, Press Enter Italic type is used for the following: Emphasis Keyboard entries when a name or variable muse be typed in place of words in italics. For example, copy file name means to type the word copy, to type a space, and then to type a file name. The plus (+) sign is used between keyboard keys to indicate that you should press the keys at the same time. For example, Press ctrl+u means to press the ctrl key and the u key at the same time. 22

23 Overview of Ansoft HFSS There are numerous ways to perform most tasks. This tutorial will show you one way. Keep in mind that with experience you will learn the other ways. There is no required sequence of events when creating a design. Design steps can be performed in any logical order. You can quickly modify design properties at any time. For example, you can change dimensions through the Properties window. You can easily track modifications to your design in the historytree and the project tree. You can modify the model view at any time. You can save time by parameterizing design properties. You can use HFSS s extensive post-processing features to evaluate solution results. 23

24 Overview of Ansoft HFSS (con t) The Ansoft HFSS window A Project Manager contains the design tree which outlines the structure of the project A Message Manager the allows you to view errors or warning A Property Window that displays and allows you to change model parameters A Progress Window that displays solution progress A 3-D Modeler Window which contains the model and model tree for the active design } } Project Design Design Setup Design Automation Design Results Other Designs The Project Window A project is a collection of one or more designs saved in a single *.hfss file. A new project is automatically created when HFSS is launched. A new project is listed in the project tree in the Project Manager window and is named Projectn by default. Project definitions, such as material assignments, are stored under the project name. 24

25 Overview of Ansoft HFSS (con t) Menu Bar Toolbars Project Manager with Project Tree 3-D Modeler Window Properties Window Message Manager Status Bar Coordinate Entry Fields (not highlighted) Progress Window 25

26 Overview of Ansoft HFSS (con t) Solution Types in HFSS Driven Modal- This solution calculates the modal-based S-Parameters. The Scattering Matrix or S-matrix solutions will be expressed in terms of the incident and reflected powers of waveguide modes Driven Terminal This solution calculates the terminal-based S-parameters of multi-conductor transmission line ports. The Scattering or S-matrix solutions will be expressed in terms of terminal voltages and currents Eigenmode This solution calculates the eigenmodes, or resonances, of a structure. The eigenmode solver finds the resonant frequencies of the structure and the fields at those resonant frequencies Convergence criterion for various solution types Driven Modal Delta S for the modal S-parameters Driven Terminal Delta S for the single-ended or differential nodal S-parameters Eigenmode Delta F where F is the frequency 26

27 Overview of Ansoft HFSS (con t) Changing the View in the 3-D Modeler Window At any time during the creation of the 3-D Model you can change the view by using: Under the menu item View Rotate The structure will be rotated around the coordinate system Pan The structure will be translated in the graphical area Dynamic Zoom Moving the mouse upwards will increase the zoom facto while moving the mouse Zoom In/Out In this mode a rubber band rectangle will be defined by dragging the mouse. After releasing the mouse the zoom factor will be applied Fit All This will zoom the defined structure to a point where it fits in the drawing area Fit Selection This fits only the selected objects into the drawing area Spin Drag the mouse and release the mouse button to start the object spinning. The speed of the dragging prior to releasing the mouse controls the speed of the spin. Animate Create or display the animation of parametric geometry Feel free to discover any one of these commands during the tutorial. Remember, Ctrl-D gets you back to the original size and holding down the Alt key and clicking the upper right hand corner of the 3-D Modeler window get you back to the normal perspective. 27

28 Simulation-Step-by-Step Procedure Outline of Simulation 1. Set up the Design Launch Ansoft HFSS, Set the Tool Option, Rename the open a New Project, Set Solution Type, Set the Units 2. Create the 3-D model Set the default material Create Substrate Create Infinite Ground Assign boundary condition Create conductor patches Create Wave ports and Excitations Set up the Radiation Boundary 3. Set up and Generate Solutions Add a solution setup to the Design Validate the Design Analyze the Design 4. Compare Solutions Create a Rectangular Plot of the Reflection Coefficient Create a Radiation Pattern and Field Plot of the Antenna 28

29 Set up the Design Launch Ansoft HFSS 1. To access Ansoft HFSS, click the Microsoft Start button, select Programs, and select the Ansoft>HFSS 10 program group. Click HFSS 10. Setting Tool Options 1. Select the menu item Tools>Options>HFSS Options 2. HFSS Options Window: a. Click the General Tab Use wizards for data entry when creating new boundaries: Checked Duplicate boundaries with geometry: Checked b. Click the OK button 3. Select the menu item Tools>Options>3D Modeler Options 4. 3D Modeler Options Window a. Click the Operation tab Automatically cover closed polylines: Checked b. Click the Drawing tab Edit property of new primitives: Checked c. Click the OK button 29

30 Set up the Design (con t) Save a New Project 1. Click File>Save As 2. Use the file browser to locate the folder in which you want to save the project and then double click the folder s name 3. Type Antenna and File Name text box and then click Save. 4. Do not forget to save your design periodically throughout the tutorial. Rename the Design 1. The design is already listed in the project tree when HFSS opens. It is named HFSS Designn by default. The 3-D Modeler window appears to the right of the Project Manager. To rename the design: Right-click HFSSDesignn in the project tree, and then click Rename on the shortcut menu. 2. Type AntennaProbe and then press Enter. Select the Solution Type 1. As you set up the design for analysis, available settings depend on the solution type. For this design, you will choose Driven Model as the solution type. To specify the design solution type, click HFSS>Solution Type 2. In the Solution Type dialog box, select Driven Terminal and then click OK. 30

31 Create the Model Set the Drawing Units 1. To set the units of measurement for drawing the geometric model. Click 3D Model>Units 2. Select cm for the Select units pull-down list and then click OK Create the 3-D Model of the Probe Feed Patch Antenna The Antenna is made of four main structures 1. Substrate 2. Infinite ground plane 3. Metallic patch 4. Coax probe feed. You will create each geometry separately and assign material properties to each. Then, prior to analysis, you will create a radiation boundary. 31

32 Create the Model (con t) Create the Substrate 1. Select the menu item Draw>Box 2. Using the coordinate entry fields (at the bottom of the screen), enter the box position: X: -5.0, Y: -4.5, Z: 0.0, Press the Enter Key 3. Using the coordinate entry fields, enter the opposite corner of the box: dx: 10.0, dy: 9.0, dz: 0.32, Press the Enter Key 4. To set the name, select the Attribute tab from the Properties window (see next slide) 5. For the Value of Name type: Sub1 6. To set the material, click the vacuum button that is in the value of the Material row. 7. Type Rogers in the Search by name field and select Rogers RT/duroid 5880 (tm) from the list and then click OK (Note: By default, the material to the box is vacuum ) 8. Click the Edit box in the Transparent row. 9. Move the slider to your preferred transparency level (about 0.6) and then click OK. 10. Click the OK button to close the Properties dialog 32

33 Create the Model (con t) To fit the view of the model 1. Select the menu item View>Fit All>Active View or press Ctrl+D. The Properties window appears, with the Command tab selected, enabling you to Modify the dimensions and position of the box. While the Properties window is open, you will use it to assign a name to the box, confirm its material assignment, an make it more or less transparent, depending on your preferences. You will notice the Properties box remains on the left hand of the screen. Name Material 33

34 Create the Model (con t) Create an Infinite Ground 1. To create the infinite ground, select the menu item Draw>Rectangle 2. Using the coordinate entry fields, enter the rectangle position: X: -5.0, Y: -4.5, Z: 0.0, Press the Enter key 3. Using the coordinate entry fields, enter the opposite corner of the rectangle: dx: 10.0, dy: 9.0, dz:0.0, Press the Enter key 4. Select the Attribute tab in the Properties dialog. 5. For the Value of Name type: Inf_GND 6. Click the OK button to close the Properties window. Assign a Perfect E boundary to the Infinite Ground 1. To select the trace, select the menu item Edit>Select>By Name 2. With the Select Object dialog open, select the object named Inf_GND 3. Click the OK button 4. To assign the Perfect E boundary, select the menu item HFSS>Boundaries>Assign>Perfect E 5. With the Perfect E Boundary window open, rename to PerfE_Inf_GND, check (select) the box for Infinite Ground Plane and click the OK button to close the window. 34

35 Create the Model (con t) Create an Infinite Ground Cut Out 1. To create the cut out, select the menu item Draw>Circle 2. Using the coordinate entry fields, enter the center position: X: -0.5, Y: 0.0, Z: 0.0, Press the Enter Key 3. Using the coordinate entry fields, enter the radius: dx: 0.16, dy: 0.0, dz: 0.0, Press the Enter Key 4. Select the Attribute tab in the Properties dialog. 5. For the Value of Name type: Cut_Out 6. Click the OK button to close the Properties window. Complete the Infinite Ground 1. To selet the objects Inf_GND and Cut_Out, select the menu item Edit>Select>By Name 2. With the Select Object dialog open, select the objects Inf_GND and Cut_Out by holding the Shift key down and click the OK button. 3. Select the menu item 3D Modeler>Boolean>Subtract 4. With the Subtract window open, move Inf_GND to Blank Parts and Cut_Out to Tool Parts if they are in the wrong column, make sure that Clone tool objects before subtract is NOT checked and click the OK button. 35

36 Create the Model (con t) Create the Patch 1. To create the patch, select the menu item Draw>Rectangle 2. Using the coordinate entry fields, enter the rectangle position: X: -2.0, Y: -1.5, Z:0.32 Press the Enter key 3. Using the coordinate entry fields, enter the opposite corner of the rectangle: dx: 4.0, dy: 3.0, dz:0.0 Press the Enter key 4. Select the Attribute tab in the Properties dialog. 5. For the Value of Name type: Patch 6. Click the OK button to close the Properties window 7. Select the menu item View>Fit All>Active View to fit the view or Crtl+D. 36

37 Create the Model (con t) Assign a Perfect E boundary to the Infinite Ground 1. To select the trace, select the menu item Edit>Select>By Name 2. With the Select Object dialog open, select the object named Patch and click the OK button 3. To assign the Perfect E boundary, select the menu item HFSS>Boundaries>Assign>Perfect E 4. With the Perfect E Boundary window open, rename to PerfE_Inf_Patch (select) the box for Infinite Ground Plane and click the OK button to close the window. Create the Coax feed 1. To create the Coax, select the menu Draw>Cylinder 2. Using the coordinate entry fields, enter the cylinder position X: -0.5, Y: 0.0, Z:0.0, Press the Enter key 3. Using the coordinate entry fields, enter the cylinder radius X: 0.16, Y: 0.0, Z:0.0, Press the Enter key 4. Using the coordinate entry fields, enter the cylinder height X: -0.5, Y: 0.0, Z: -0.5, Press the Enter key 5. Select the Attribute tab in the Properties dialog. 6. For the Value of Name type: Coax 7. Click the OK button to close the Properties window 8. Select the menu item View>Fit All>Active View to fit the view. 37

38 Create the Model (con t) Create the Coax Pin 1. Select the menu item Draw>Cylinder 2. Using the coordinate entry fields, enter the cylinder position: X: -5.0, Y: -4.5, Z: 0.0, Press the Enter Key 3. Using the coordinate entry fields, enter the cylinder radius: dx: 0.07, dy: 0.0, dz: 0.0, Press the Enter Key 4. Using the coordinate entry fields, enter the cylinder height: dx: 0.0, dy: 0.0, dz: -0.5, Press the Enter Key 5. To set the name, select the Attribute tab from the Properties window 6. For the Value of Name type: coax_pin 7. To set the material, click the vacuum button that is in the value of the Material row. 8. Type pec in the Search by name field and select pec (perfect electrical conductor) from the list and then click OK 9. Click the OK button to close the Properties dialog 38

39 Create the Model (con t) Create the Wave Port 1. To create a circle that represents the port, select the menu item Draw>Circle 2. Using the coordinate entry fields, enter the circle position: X: -5.0, Y: 0.0, Z: -0.5, Press the Enter Key 3. Using the coordinate entry fields, enter the circle radius: dx: 0.16, dy: 0.0, dz: 0.0, Press the Enter Key 4. To set the name, select the Attribute tab from the Properties window 5. For the Value of Name type: port1 6. Click the OK button to close the Properties dialog Plot of the Electric Field at Wave Port Wave Port Close-up of Coaxial Antenna Feed 39

40 Create the Model (con t) Assign Wave Port Excitation 1. Select the menu item HFSS>Excitations>Assign>Wave Port 2. In Wave Port: General, type the name p1 and click the next button 3. In Wave Port: Terminals a. Number of Terminals: 1 b. For T1: click Undefined column and select New Line c. Using the coordinate entry fields, enter the vector position X: -0.34, Y: 0.0, Z: -0.5, Press the Enter key d. Using the coordinate entry fields, enter the vertex dx: -0.09, dy: 0.0, dz: 0.0, Press the Enter key 4. In Wave Port: Differentials: leave settings and press the Next button 5. In Wave Port: Post Processing set the Reference Impedance to Click the Finish button Bottom View of Coaxial Feed Vector defining the polarity 40

41 Create the Model (con t) More on Excitations In the previous step, you defined a wave port. Ports and a unique type of boundary condition that allow energy to flow into and out of a structure. In HFSS, you can assign a port to an 2- D or 3-D object face. Before the full 3-D EM field inside a structure can be calculated, it is necessary to determine the excitation field at each port. HFSS uses an arbitrary port solver to calculate the natural field patterns or modes that can exist inside a transmission structure with the same cross section as the port. The resulting 2-D field patterns serve as boundary conditions for the full 3-D problem. The port solver assumes that the Wave Port you have defined is connected to a semiinfinitely long transmission line (coaxial in this case) with the same cross-section and material properties. The field pattern of the traveling wave inside the Wave Port is calculated using Maxwell's equations. In this case, the excitation (coax probe) is a transverse electromagnetic (TEM) transmission line, therefore it is necessary to define a Terminal Line for each conductor across a port. In general a single terminal line is created from the reference of ground conductor to each port-plane conductor. The polarity reference for the voltage is established by the arrow head (+) to the base (-) of the terminal line. In this case, the vector was drawn from the outer conductor of the coaxial cable to the inner conductor. 41

42 Create the Model (con t) Create the Probe 1. Select the menu item Draw>Cylinder 2. Using the coordinate entry fields, enter the cylinder position: X: -0.5, Y: 0.0, Z: 0.0, Press the Enter Key 3. Using the coordinate entry fields, enter the cylinder radius: dx: 0.07, dy: 0.0, dz: 0.0, Press the Enter Key 4. Using the coordinate entry fields, enter the cylinder height: dx: 0.0, dy: 0.0, dz: 0.32, Press the Enter Key 5. To set the name, select the Attribute tab from the Properties window 6. For the Value of Name type: probe 7. To set the material, click the vacuum button that is in the value of the Material row. 8. Type pec in the Search by name field and select pec (perfect electrical conductor) from the list and then click OK 9. Click the OK button to close the Properties dialog 42

43 Create the Model (con t) Create Air around the Antenna 1. Select the menu item Draw>Box 2. Using the coordinate entry fields, enter the box position: X: -5.0, Y: -4.5, Z: 0.0, Press the Enter Key 3. Using the coordinate entry fields, enter the opposite corner of the box: dx: 10.0, dy: 9.0, dz: 3.32, Press the Enter Key 4. To set the name, select the Attribute tab from the Properties window 5. For the Value of Name type: air 6. Make sure the material is set at vacuum in the value of the Material row. 7. Click the Edit box in the Transparent row. 8. Move the slider to transparency level to 1 and then click OK. 9. Click the OK button to close the Properties dialog 10. Select the menu item View>Fit All>Active View to fit the view 43

44 Create the Model (con t) Create Radiation Boundary 1. To pick the faces, select the menu item Edit>Select>Faces 2. Graphically select all of the faces of the Air object except the face at z = 0.0 cm (use the Ctrl key to select multiple faces at a time and the B button to select behind a selected face) 3. To create the radiation boundary, select the menu item HFSS>Boundaries>Assign>Radiation 4. In the Radiation Boundary window, enter the name Rad1 and click the OK button Side View (XZ Plane) 3-D View 44

45 Create the Model (con t) Create a Radiation Setup 1. To define a radiation setup, select the menu item HFSS>Radiation>Insert Far Field Setup>Infinite Sphere 2. In the Far Field Radiation Sphere Setup dialog, make the following settings: Name: ff_2d Phi: Start: 0, Stop: 90, Step Size: 90 Theta: Start: -180, Stop: 180, Step Size: 2 3. Click the OK button to close the dialog 4. Define another radiation field, select the menu item HFSS>Radiation>Insert Far Field Setup>Infinite Sphere again 5. In the Far Field Radiation Sphere Setup dialog, make the following settings: Name: ff_3d Phi: Start: 0, Stop: 360, Step Size: 2 Theta: Start: 0, Stop: 180, Step Size: 2 6. Click the OK button to close the dialog 45

46 Analyze the Model Analysis Setup 1. To create an analysis setup, select the menu item HFSS>Analysis Setup> Add Solution Setup 2. In the Solution Setup window, click the General tab and enter Solution Frequency: 2.5 GHz Maximum Number of Passes: 20 Maximum Delta S per Pass: Click the OK button 46

47 Analyze the Model (con t) Adding a Frequency Sweep 1. To add a frequency sweep, select the menu item HFSS>Analysis Setup>Add Sweep 2. Select Solution Setup: Setup1 and Click the OK button. 3. Edit the Sweep Window by entering the following values: Sweep Type: Fast Frequency Setup Type: Linear Count Start: 1.0 GHz Stop: 3.5 GHz Count: 201 Save Fields: Checked 4. Click the OK Button Save Project 5. If you have not been saving your file, select File>Save Model Validation 1. To validate the model, select the menu item HFSS>Validation Check 2. Click the Close button (To view any errors or warning messages, use the message manager at the bottom of the screen) Analyze 1. Congratulations you are ready to analyze. To start the solution process, select the menu item HFSS>Analyze 47

48 View the Solution Data Solution Data 1. To view the Solution Data, select the menu item HFSS>Results>Solution Data 2. Click the Profile tab to view the solution profile (elapsed time, mesh generation statistics, etc.) 3. Click the Convergence tab to view solution convergence as a function of pass number and the number of tetrahedra used. Note the total number of passes. Click Plot. 4. Click the Matrix Data tab to view the data. 5. Click the Close button 48

49 Create Reports Create a report that plots the input return loss vs. frequency 1. To create this report, select the menu item HFSS>Results>Create Report 2. In the Create Report Window, select: Report Type: Terminal Solution Data Display Type: Rectangular Plot 3. Click the OK button 4. In the Traces window, select the following: Solution: Setup1: Sweep 1 Domain: Sweep 5. Click the Y tab and select: Category: Terminal S Parameter Quantity: St(p1,p1) Function: db 6. Click the Add trace button 7. Click the Done button 8. Use the Data Marker to find the resonant frequency of the structure. 49

50 Create Reports (con t) Create a 2-D plot of the far field pattern 1. To create a 2-D polar far field plot, select the menu item HFSS>Results>Create Report 2. In the Create Report Window, select: Report Type: Far Fields Display Type: Radiation Pattern 3. Click the OK button 4. In the Traces window, set the following: Solution: Setup1:Sweep1 Geometry: ff_2d 5. In the Sweeps tab, select Phi under the Name column, and on the drop list, select Theta. This changes the primary sweep to Theta. 6. In the Sweeps tab, select the row labeled Freq and select the resonant frequency from the list 7. In the Mag tab,select: Category: Gain Quantity: Gain Total Function: db 8. Click the Add Trace button 9. Click the Done button 50

51 Create Reports (con t) Create a 3-D plot of the far field pattern 1. To create a 3-D polar far field plot, select the menu item HFSS>Results>Create Report 2. In the Create Report Window, select: Report Type: Far Fields Display Type: 3D Polar Plot 3. Click the OK button 4. In the Traces window, set the following: Solution: Setup1:Sweep1 Geometry: ff_3d 5. In the Sweeps tab, select the row labeled Freq and select the resonant frequency from the list 6. In the Mag tab,select: Category: re Quantity: re Total Function: <none> 7. Click the Add Trace button 8. Click the Done button 51

52 Create a Field Plot Create a Magnitude Magnetic Field Plot on the substrate 1. To create a Magnetic Field Plot, return to the 3-D Modeler Window by selecting HFSS>3D Model Editor. Note: This step is only necessary if you have a Plot window open. 2. Switch to face selection mode by clicking Edit>Select>Faces 3. Select the top face of the substrate. You may need to use the B button to select the face behind the current selection. 4. To open the Create Field Plot window, click HFSS>Fields>Fields>H>Mag_H 5. Select Setup1:LastAdaptive as the solution to plot in Solution pull-down list 6. Accept the default settings by clicking Done 52

53 Create Field Plot (con t) Animate the Field Overlay Plot An animated plot is a series of frames that displays a field, mesh, or geometry at varying values. You specify the values of the plot that you want to include, called a frame. 1. Right-click Mag_H1 in the Project Tree, and then click Animate 2. In the Setup Animation window, click the Swept Variable tab: Name: AnimationH 3. Click the OK button Swept Variable: Phase Start: 0deg Stop: 180deg Steps: 6 4. After viewing the animation, click the stop button in the Animation dialog that has appeared in the upper left hand corner 53

54 Create a Mesh Plot Create a Mesh Plot on the substrate 1. To create a Magnetic Field Plot, return to the 3-D Modeler Window by selecting HFSS>3D Model Editor. Note: This step is only necessary if you have a Plot window open. 2. Switch to face selection mode by clicking Edit>Select>Faces 3. Select the top face of the substrate. You may need to use the B button to select the face behind the current selection. 4. To open the Create Field Plot window, click HFSS>Fields>Plot Mesh 5. Select Setup1:LastAdaptive as the solution to plot in Solution pull-down list 6. Accept the default settings by clicking Done 7. You may wish to delete the previous Field Plot from the figure by right clicking the H field under Field Overlays in the Project Manager Tree. This concludes the tutorial 54

55 Further Reading and References Electromagnetics N.N. Rao, Elements of Engineering Electromagnetics, Pearson Prentice Hall, Upper Saddle River, NJ, 2004 W.H. Hayt and J.A. Buck, Engineering Electromagnetics, McGraw-Hill, New York, NY, 2006 Computational Electromagnetics A. Taflove and S. Hagness, Computational Electrodynamics: The Finite Difference Time Domain Method, Artech House, Boston, MA, 2000 J.Jin, The Finite Element Method in Electromagnetics, 2 nd edition, Wiley, New York, NY, 2002 P.P Silvester and R.L. Ferrari, Finite Elements for Electrical Engineers, 3 rd edition, Cambridge University Press, Cambridge, 1996 Antennas C.A. Balanis, Antenna Theory, Analysis and Design, 3 rd edition, Wiley, New York, NY, 2005 J.D. Kraus and R.J. Marhefka, Antennas for All Applications, 3 rd edition, McGraw-Hill, New York, NY,